The foramen ovale is a "flap" of tissue which is part of the wall separating the two small pumping chambers (the atriums) of the heart. In the fetus the flap is pushed wide open, allowing blood in the right atrium to cross to the left atrium - a normal part of the circulation before birth. After birth the pressure in the left atrium increases and the flap is pushed closed, although often it is not quite "watertight", so that in small babies it is frequently possible to detect a little blood flowing across it on an ultrasound scan of the heart. When blood flow across the foramen (in either direction) is detectable this is known as a patent foramen ovale. Many adults have a PFO - perhaps as many as one in ten of the normal population, and the PFO is almost always harmless.
Stroke and PFO
With increasing age it is possible that small blood clots form in the veins in the legs, even in people who are otherwise completely well. If a blood clot in the leg breaks away and floats along with the bloodstream it reaches the heart, and in most people it would then usually get pumped to the lungs. This may cause very little in the way of symptoms unless the blood clot is big. However, in a patient with a PFO there is a chance that the blood clot might reach the heart and cross the PFO to reach the left side of the heart, where the clot can get pumped to the body instead of to the lungs. If the clot then happens to be carried to the arteries which feed blood to the brain, it can block a small artery in the brain itself, stopping blood getting to that part of the brain. If the artery remains blocked, the area of the brain which is fed by that artery will die. This is known as a stroke and will cause symptoms such as weakness down one side of the body or difficulty with speech. If multiple strokes occur the brain becomes more damaged and the patient is likely to be permanently handicapped and may even die.
Most strokes are caused by disease in the arteries ("atherosclerosis") causing the arteries to become narrow and sometimes to block completely, or by heart disease causing blood clots to form inside the heart. Patients who have had a stroke usually have tests to look for narrow arteries and heart disease but, particularly in young adults, sometimes no cause can be found but a PFO is detected. It is often very difficult in such cases to know whether the PFO has played a part in causing the stroke or not - although we know that it is possible for blood clots to pass through a PFO to cause a stroke, we also know that many normal adults who have not had strokes also have a PFO. Having a stroke is very frightening and is potentially serious, so when no cause can be found except for a PFO, it seems reasonable to think about closing the PFO in the hope of reducing the chances of the patient having further strokes in the future - even though we do not know for sure that it is the real cause of the problem. Patients who have had a stroke with no definite cause found have a risk of having a further stroke of approximately 4 strokes per 100 patients per year. Research has suggested that closing a PFO in a large group of patients might reduce the overall chances of having another stroke, but will not guarantee prevention in any one particular patient.
PFOs can be closed using an operation to stitch the edges together, or by using a newer keyhole technique where a specially designed "button" is placed in the PFO through a long tube inserted into the vein at the top of the leg. If you decide you want us to close your PFO it is important that you understand that, although PFO closure may reduce the risk of another stroke, it does not guarantee that another stroke will not occur. Surgery involves a scar down the centre of the chest. For the surgeon to close the PFO the heart has to be stopped for a short time and its function is taken over by a mechanical pump while the surgeon stitches the PFO closed. There is a small (about 1 in 100) risk of dying at operation and also a small (about 1 in 100) risk of the operation itself causing a stroke. Usually surgery involves about 10 days in hospital and it takes about 2 to 3 months for the patient to recover fully and return to work. Keyhole treatment was introduced in Leeds in 1997. The button used to close the PFO is guided into place using X-ray pictures and sometimes using a "transoesophageal" ultrasound scan (a “TOE”, done using a probe down the patient’s throat). If a PFO appears simple to close it may be possible to have the procedure done under local anaesthetic, but if a TOE is needed the procedure is usually done under general anaesthetic because it can be uncomfortable lying still with the probe down the throat for the time necessary to complete the procedure (up to an hour). Keyhole treatment, like surgery, carries a very small risk of death or stroke, but so far it appears that the risks are smaller than with surgery (although it will be many years before we know that for certain). There is also a very small chance (probably around 1 in 400) of other complications occurring, such as the button moving out of place after it has been put into the PFO. If that happens surgery is almost always necessary to retrieve the button as well as to stitch the PFO closed. Some patients who have suffered from migraine in the past find that their migraine is worse for a few months after keyhole closure of their PFO, and some patients find their migraine disappears after keyhole treatment. The reasons for a change in pattern of migraine are not fully understood. After keyhole treatment most patients need only one night in hospital and are usually completely back to normal activities within a few days. Medicines to reduce the chances of blood clots forming on the button are usually given for about 3 months after the procedure, by which time the button will be covered by a smooth layer of scar tissue as part of the normal healing process. We often recommend that low dose aspirin should be continued for the rest of the patient’s life, even after successful surgical or keyhole PFO closure.
How to interpret the survival funnel plots
These graphs show the national average survival after specific procedures for treating congenital heart disease. The national average is shown as a horizontal grey line. Two control limits are shown; a warning limit (Green line, 98%) and an alert limit ( Red line 99.5%). Unit performances are shown as identifiable coloured symbols. If a unit's symbol is above the green line then the performance is no different from the national average. If a unit’s survival rate is below the warning limit, their performance will be closely monitored in subsequent years. If a unit’s survival rate is below the alert limit, an investigation into possible reasons and remedial actions will be launched by the appropriate professional and regulatory bodies.